Chemical-mechanical polishing pad with textured platen adhesive

ABSTRACT

A chemical-mechanical polishing pad comprising a removable platen adhesive comprising a textured surface. A method of using the polishing pad to eliminate or reduce the occurrence of spot balding on the surface of the polishing pad.

BACKGROUND OF THE INVENTION

An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. A variety of fabrication processes require planarization of a layer on the substrate. For example, for certain applications, e.g., polishing of a metal layer to form vias, plugs, and lines in the trenches of a patterned layer, an overlying layer is planarized until the top surface of a patterned layer is exposed. In other applications, e.g., planarization of a dielectric layer for photolithography, an overlying layer is polished until a desired thickness remains over the underlying layer. Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing liquid, such as slurry with abrasive particles, is typically supplied to the surface of the polishing pad.

Polishing pads are typically made by extrusion, molding, casting or sintering polyurethane materials. In the case molding, the polishing pads can be made one at a time, e.g., by injection molding. In the case of casting, the liquid precursor is cast and cured into a cake, which is subsequently sliced into individual pad pieces. These pad pieces can then be machined to a final thickness. Grooves can be machined into the polishing surface or can be formed as part of the injection molding process.

Polishing pads may be multilayered, or stacked, pads. Multilayer pads may have a polishing pad layer adhered to a rigid layer, or directly to a subpad or base layer. The polishing layer and the rigid or subpad layers are adhered together with the use of an adhesive, typically a permanent adhesive, such as a hot melt adhesive. The rigid or the subpad layer has a surface opposite of the surface that is adhered to the polishing layer or stack, and this surface typically has an adhesive for adhering the pad to the platen of the polishing tool. This platen adhesive is typically a temporary, or removable, adhesive with respect to the surface of the platen and the of the subpad layer. The composition of the temporary adhesive is an important consideration, as the adhesive must keep the polishing pad fixed to the platen during the polishing process where chemicals in the polishing slurry and the heat generated may degrade the adhesive. The temporary adhesive must also allow for easy removal of the worn pad following a certain number of polishing steps.

The polishing surface of the polishing pad is conditioned during the polishing process. The conditioning, or dressing, is critical to maintain a consistent polishing surface for uniform polishing performance. During the polishing process the polishing surface of the polishing layer is wears down, forming a glaze or an undesirable smooth surface lacking microtexture. The conditioning step is typically achieved by dragging a conditioning disk across the polishing surface of the pad, with a downforce, to mechanically abrade the pad surface thereby removing debris and forming a microtexture. The conditioning disk typically has a surface comprised of embedded diamond particles that cut the pad surface to generate micro-asperities and renew the polishing texture. This conditioning process is necessary but reduces pad life by removing pad material from the surface. Because the conditioning process abrades material from the polishing surface, and the pad material abrasion is proportional to the downforce, differences in the height of the pad with respect to the platen surface will create an uneven abrasion across the surface of the polishing layer. Therefore, uniformity in height, or planarity, is required to achieve a uniform wear across the pad surface.

The rigid layer of a multilayered polishing pad may be an intermediate layer or the bottom most layer in the stacked pad. Alternatively, a subpad layer may the bottom most layer. In either case, the polishing pad design will vary and will be designed to address a polishing process requirement. For example, the rigid or subpad layer may vary in compressibility and hardness depending on the polishing requirements. Polishing pads with softer polishing layers adhered to hard, rigid or subpad layers are well known in the art. Additionally, polishing pads with softer, more compressible subpad layers are also known and have advantages for certain polishing procedures. It has been observed by the present inventors, that softer, more compressible subpad layers may present difficulty in getting the pads perfectly planar when adhering to the platen surface. Therefore, the need exists to find an improved a polishing pad having a softer, less compressible backing layer, that will easily adhere to a platen surface and be planar.

BRIEF SUMMARY OF THE INVENTION

The invention provides a polishing pad comprising a removable platen adhesive, where the adhesive has a textured surface. The invention also provides a chemical-mechanical polishing pad comprising a polishing pad body having a polishing surface and a back surface opposite of the polishing surface, wherein a removable platen adhesive is secured to the back surface, the platen adhesive having a textured surface.

The invention further provides a polishing pad comprising a polishing layer attached to a backing layer, the polishing layer having a polishing surface, the backing layer having a surface opposite the polishing surface, a platen adhesive secured to the backing layer surface opposite the polishing surface, wherein the platen adhesive has a textured surface.

The invention further provides chemical-mechanical polishing pad having a less rigid body comprising a textured platen adhesive secured to a surface of the polishing pad.

The invention further provides a method of affixing a chemical-mechanical polishing pad to a platen surface comprising: (a) securing a platen adhesive having a textured surface to the polishing pad, (b) attaching the polishing pad to the platen surface by pressing the textured surface of the platen adhesive to the platen surface, wherein the textured surface of the platen adhesive allows air to escape without being trapped between the platen surface and the polishing pad.

The invention further provides a method of affixing a chemical-mechanical polishing pad having a less rigid body to a platen surface comprising: (a) securing a platen adhesive having a textured surface to the polishing pad, (b) attaching the polishing pad to the platen surface by pressing the textured surface of the platen adhesive to the platen surface, wherein the textured surface of the platen adhesive allows air to escape without being trapped between the platen surface and the polishing pad.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 illustrates and example of spot balding on a groove polishing surface.

FIG. 2 depicts one embodiment for a configuration of a polishing pad of the present invention.

FIG. 3 depicts an exploded view of the platen adhesive layer.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a polishing pad with a textured, removable platen adhesive. The textured platen adhesive may comprise grooves or microchannels that prevent spot balding and premature pad wear. This invention also provides a method of preventing spot balding and premature pad wear in a polishing pad by using polishing pad comprising a removable, textured platen adhesive.

The polishing pad of the present invention may be a unitary pad or a multilayered pad. When the polishing pad is a multilayered pad, the pad may consist of 2 or more layers bonded together with an adhesive. Pads having multiple layers may also be of a unitary construction in which the multiple layers are covalently bonded to one another through an integral interface. In some embodiments, as disclosed herein, the pads are unitary and therefore have an integral interface through which layers are covalently bonded to one another.

Multilayered polishing pads of the present invention may comprise a polishing layer adhered to a rigid backing layer and/or to a subpad layer. In some embodiments, the polishing pads of the present invention will comprise a polishing layer (also referred to as a top sheet), adhered to a rigid backing (also referred to as foundation) layer, which is adhered to a subpad layer. In other embodiments, the polishing layer is adhered to a subpad layer. In yet other embodiments, the polishing layer is adhered to a rigid backing layer, without a subpad layer.

In other embodiments, the unitary polishing pad, as disclosed herein, is defined as a polishing pad with a single layer of a uniform material, or a homogeneous composition. In an embodiment, the homogeneous body is composed of a thermoset, closed cell polyurethane material. In the context of the present invention, the term “homogeneous” is used to indicate that the composition of a thermoset, closed cell polyurethane material is consistent throughout the entire composition of the body. For example, in an embodiment, the term “homogeneous” excludes polishing pad bodies composed of, e.g., impregnated felt or a composition (composite) of multiple layers of differing material.

Regardless of whether the polishing pad is a unitary, single layer pad or a multilayer pad, the polishing pad will consist of a polishing surface and a back surface opposite the polishing surface. The back surface that is opposite of the polishing surface will be the surface that will contain the textured platen adhesive of the present invention, thus securing (e.g., adhering) the polishing pad to the platen of the polishing tool.

In an embodiment, the term “thermoset” is used to indicate a polymer material that irreversibly cures, e.g., the precursor to the material changes irreversibly into an infusible, insoluble polymer network by curing. For example, in an embodiment, the term “thermoset” excludes polishing pads composed of, e.g., “thermoplast” materials or “thermoplastics”—those materials composed of a polymer that turns to a liquid when heated and returns to a very glassy state when cooled sufficiently. It is noted that polishing pads made from thermoset materials are typically fabricated from lower molecular weight precursors reacting to form a polymer in a chemical reaction, while pads made from thermoplastic materials are typically fabricated by heating a pre-existing polymer to cause a phase change so that a polishing pad is formed in a physical process. Polyurethane thermoset polymers may be selected for fabricating polishing pads described herein based on their stable thermal and mechanical properties, resistance to the chemical environment, and tendency for wear resistance.

The present invention may include a subpad as part of the polishing pad. Any suitable subpad may be used, for example, subpads may include polyurethane foam subpads, impregnated felt subpads, microporous polyurethane subpads, and sintered urethane subpads. The subpad optionally comprises grooves, channels, hollow sections, windows, apertures, and the like. The subpad can be affixed to the polishing layer by any suitable means. For example, the polishing layer and subpad can be affixed through adhesives or can be attached via welding or similar technique.

The rigidity of a polishing pad may affect the tendency of the pad to form bubbles caused by trapped air during pad installation. A thicker pad tends to be more rigid, but other factors such as the material used or the use of a backing layer. A rigid pad tends to trap less air bubbles compared to a less rigid pad, and thus is less susceptible to spot balding. However, all polishing pads are capable of forming trapped air bubbles during installation. Pads that are less rigid tend to form trapped air bubbles easily, and thus are very prone to spot balding. The rigidity of a polishing pad, as used herein, is the rigidity of the entire pad, whether it is a multi-layer pad or uniform pad. Rigidity in a pad may be measured by any suitable method. For example, a stress strain universal tester may be used. A stress strain universal tester measures the force needed to deflect a long and large pad sample (for example a 12 inch by 5 inch sample). The test pad sample may comprise the top pad, the subpad, the adhesive layer and also the release liner. The deflection is typically on the order of 2 to 3 inches. These large dimensions are used in order to closely simulate a pad installation process.

As used herein, a less rigid pad is defined as a pad having a lower force need to deflect the pad sample as compared to a control pad sample.

The polishing pad of the present invention comprises removable or temporary adhesive, for example, a pressure sensitive platen adhesive. The removable pressure sensitive platen adhesive layer facilitates mounting of the unitary or multilayer chemical mechanical polishing pad, or pad stack, on a polishing machine. The platen adhesive of the present invention may be any suitable material. The platen adhesive is preferably resistant to the heat and chemicals typically used in chemical-mechanical polishing processes. For example, the adhesive should maintain the adhesive property and not allow the polishing pad to detach from the platen surface during the chemical-mechanical polishing process.

The present invention also provides various transfer tapes, also called double sided adhesive tape, that include the platen adhesive and a pad adhesive. The transfer tapes comprise one or more layers of the adhesives on a carrier film and a liner, such as a release liner, for each adhesive face. In certain embodiments the transfer tapes have a permanent type adhesive on one side of the tape and the grooved platen adhesive on the opposite side. This embodiment is depicted in FIGS. 2 and 3. In other embodiments, the transfer tape may have the identical adhesive on both sides, but only the platen side will have the grooved, or textured surface.

The carrier film of the transfer tape may be any suitable material. For example, the carrier film may be a polyethylene terephthalate (PET). Additionally, the carrier film may have any suitable thickness. For example, the carrier film may have a thickness of about 0.5 mil to about 2.0 mil.

The release liner may be any suitable material and thickness. For example, the release liner may be a polyester material and may have a thickness of about 2 mil to about 5 mil. In an embodiment of the present invention, the release liner is textured or grooved such that the pattern on the release liner is imprinted on the adhesive, and the adhesive, at least temporarily retains the shape of the groove or texture imprinted by the release liner once the release liner is removed. In this embodiment, the release liner of the polishing pad would be removed just prior to the installation of the pad on the platen.

The micro-channels of the present invention can take various shapes or patterns. The micro-channels are generally formed by structures in the adhesive that create the microstructured surface. The structures may be either placed randomly about the surface of the adhesive or placed in regular textured patterns.

The textured pattern on the release liner may be any suitable pattern that prevents air being trapped under the polishing pad during installation. For example, the pattern in the release liner may be a micro-channel pattern that consists of an XY pattern. Alternatively, the pattern may be a microchannel created by a series of connected honeycombs, diamond shapes or other geometric designs. The dimensions of the micro-channels may be any suitable dimensions, provided that the micro-channels allow the air to escape during the installation of the polishing pad. For example, the channel depth may range from about 5 μm to about 250 μm. For example, the channel depth may be about 5 μm or greater, about 10 μm or greater, about 15 μm or greater, about 20 μm or greater, about 25 μm or greater, about 30 μm or greater, about 40 μm or greater. For example, the channel depth may be about 250 μm or less, for example, about 200 μm or less, about 150 μm or less, about 100 μm or less, about 50 μm or less. Preferably, the channel depth ranges from about 20 μm to about 50 μm. The micro-channel may have any suitable pitch. The pitch of the channel is correlated with the maximum size of an air bubble that will not become trapped. The channel pitch may be about 0.1 mm or greater, for example, 0.2 or greater, 0.5 mm or greater, 1.0 mm or greater, 5 mm or greater. The channel pitch may be about 10 mm or less, for example, 8 mm or less, 7 mm or less, 6 mm or less. In one embodiment, the channel pitch ranges from 1 mm to 5 mm.

The platen adhesive may be any suitable removable adhesive material that allows the polishing pad to be easily removed when worn but will securely hold the polishing pad in place during polishing operations. For example, the platen adhesive may be an acrylic resin adhesive, a rubber-based adhesive, a urethane resin adhesive or a silicon resin adhesive. These adhesives are generally low tack, removable adhesives.

Typically, the adhesive when incorporated in a transfer tape is in the form of a single uniform and continuous layer having a thickness of from about 0.5 mil to about 20 mil, and more particularly from about 1.0 mil to about 10 mil. The present subject matter also includes the use of patterned adhesives and multiple layers of the adhesives in the transfer tapes.

The platen adhesive may be applied to the polishing pad in a lamination step using a double coated tape. Suitable double coated tapes include 3M 456CR, 3M 442F and Avery 8603. Methods of laminating a double coated tape to a pad surface are well known. The double coated tape may be laminated to a polishing pad by using any suitable lamination machine, for example, an AGL laminator (Advanced Greig Laminators, Inc., DeForest, Wisconsin), and by following supplier's recommended processes.

The textured surface, for example the microchannels, can be formed by directly embossing the pressure sensitive adhesive layer with the structures. Alternatively, a liner or backing can be embossed first and then coated with a pressure sensitive adhesive to impart the structures to the adhesive. The film may be laminated or bonded to a side of the adhesive layer opposite the textured surface features.

It is an advantage of the present invention to provide a platen adhesive-backed polishing pad that has a textured surface, such that pathways are formed in the platen adhesive useful for air egress. The texture, or micro-channels define pathways to the periphery of the polishing that permit the flow of air between the platen adhesive layer and the surface of the platen. In one embodiment, the microchannel pathways end very close to, but not at the periphery. In this embodiment, the air is still permitted to escape and no air is trapped between the polishing pad and the platen.

The micro-channels of the present invention at least partially disappear upon final application of the polishing pad to the platen, in order to provide a desirable adhesion. The ability of the micro-channels to at least partially disappear is dependent upon the shape of the micro-channel and the rheology of the adhesive.

The ability for the microchannel platen adhesive to maintain the microchannels after the release liner has been removed is referred to as the channel lifetime. For example, an adhesive with a long channel lifetime will maintain the microchannel structure for several minutes after the release liner is removed, and possibly even after the polishing pad has been applied to the platen surface. The polishing pads of the present invention preferably have a channel lifetime that is sufficiently long to maintain the channel structure until the polishing pad is pressed against the platen surface during installation. Under these conditions, air will escape during the installation of the pad, but once installed, there will not be open channels at the end of the pad that could possibly allow the polishing slurry or water to enter underneath the pad.

The present invention provides a chemical-mechanical polishing pad that avoids premature wear caused by spot balding. The polishing pads of the present invention comprise a removal adhesive to adhere the pad to a platen, and the adhesive has a texture surface such that a polishing pad may be installed without trapping air. The trapped air between the platen surface and the polishing pad that happens during the installation process results in bulges in the polishing surface. The textured surface of the adhesive results in less or no air being trapped.

The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope.

EXAMPLE 1

This example demonstrates the differences in rigidity of polishing pads of varying thickness and composition.

Various polishing pad materials were tested for rigidity using a pad deflection test. The test used sections of test pads cut into a rectangular shape of dimensions length: 12.5 inches and width: 5.5 inches. The test pad sections were mounted on a Universal tester (Test Resources, Shakopee, MN) operating in the stress strain mode that is capable to measure the force required to bend the test pad sample 3 inches. Each test strip was tested 5 times and the results were averaged together.

The results of the deflection test are shown in Table 1. The results indicate that thicker pads and pads having a rigid subpad or backing layer have a higher force needed for three inches of deflection, and therefore are considered more rigid. The difference in the thickness of the subpad plus the thickness of the top pad, minus the total thickness, is the thickness of the adhesive layer between the subpad and top pad.

TABLE 1 Comparative rigidity measurements of various pads. Top Pad Total Pad Ave. Max Pad Platen Thickness Thickness Force Sample Subpad Adhesive (mil) (mil) (lbf) 1 30 mil Planar, 65 110 0.40 removable 2 30 mil microchannel 65 110 0.45 3 30 mil Planar, low 65 110 0.35 tack 4 30 mil, Planar, 65 110 0.40 dense removable 5 15 mil Planar, 65 105 0.22 removable 6 15 mil Planar, 65 105 0.22 removable 7 15 mil Planar, 65 105 0.26 removable 8 30 mil Planar, 100 145 1.02 removable 9 None Planar, very 130 135 0.67 low tack 10 Suba4, Planar, 80 140 0.80 rigid, removable (IC1010)

EXAMPLE 2

This example demonstrates the effect of a micro-channel adhesive on pad wear under aggressive polishing conditions.

Identical polishing pads were compared using different platen adhesives. E6088 polishing pads (Cabot Microelectronics, Aurora IL) were laminated with either a micro-channel adhesive (2B) or with a planar adhesive (2A and 2C). The rigidity of the differently configured E6088 pads are demonstrated in Example 1. As a comparative, the commercially available polishing pad IC1010 (Rohm and Haas Electronic Materials) was used. The rigidity of the IC1010 is shown in Example 1. The IC1010 was the most rigid of the pad materials tested.

The polishing pads were tested under the following conditions using a commercially available, silica based, polishing slurry D9228 (Cabot Microelectronics), and TEOS blanket wafers. The polishing tests used a CTS polisher model AP 300 (Creative Technology Solutions) using a platen speed of 120 rpm, a polishing downforce of 4 psi, with a slurry feed rate of 250 ml/minute. The pads were conditioned with a commercially available CMP diamond conditioner at a pressure of 121 bf. Each pad was used for 4-5 hours of polishing, followed by analysis for wear. The pads were visually inspected for wear on the polishing surface. Areas of excessive wear, for example, areas where no groove structure was visible, were counted as pad balding spots (spot balding counts), and the number of pad balding spots were recorded. FIG. 1 shows an example of visible pad wear that is considered a spot balding count.

Table 2 below shows the pad balding spot counts for the tested pads. As is apparent in the table, the E6088 pad with a micro-channel adhesive had no balding spots, while the same pad with the planar adhesive, had a significant increase in that number with 6 balding spots. Additionally, the E6088 pad with a rigid subpad also showed no balding spots.

TABLE 2 Spot balding counts for various polishing pads. Spot balding Polishing Pad Description counts IC1010, commercial Rigid pad, planar adhesive 0 pad 2A Less rigid pad, 30 mil subpad, 6 planar adhesive 2B Less Rigid pad, 30 mil subpad, 0 micro-channel adhesive 2C Rigid pad, dense 30 mil subpad, 0 planar adhesive

As is apparent from the data presented in this example, polishing pads that are less rigid, and with a planar adhesive, have problems with spot balding (2A). The use of an adhesive having micro-channels prevents the spot balding defects in less rigid polishing pads (2B).

EXAMPLE 3

This example sets forth the effect of a micro-channel adhesive on pad spot balding under simulated accelerated wear conditions.

Polishing pads determined as being less rigid from the deflection test are laminated with a non-textured removable platen adhesive or a microchannel platen adhesive. Additionally, rigid polishing pads are laminated with a non-textured removable platen adhesive and a microchannel platen adhesive. The rigid polishing pads are installed on a platen with less care than would normally be used. This is done to increase the chance of trapping air bubbles during installation. The cutting machine is a computer numerical control cutting machine (such as a Multicam CNC cutting machine) that removes a uniform depth of about 0.020″ of the pad top layer. This test provides an accelerated wear test to identify spot balding areas due to trapped air bubbled between the polishing pad and the platen.

The results of the accelerated test are identical to that of the polishing tests. The microchannel platen adhesive eliminates problems with spot balding in less rigid pads, or with more rigid pads that are installed with less care.

All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. 

We claim:
 1. A chemical-mechanical polishing pad comprising; a polishing pad comprising a polishing surface, a back surface opposite the polishing surface, a platen adhesive attached to the back surface, wherein the platen adhesive has a textured surface, and comprises a removable adhesive.
 2. The polishing pad of claim 1, wherein the textured surface of the platen adhesive comprises a microchannel texture having microchannels.
 3. The polishing pad of claim 2, wherein the microchannel texture comprises an XY pattern.
 4. The polishing pad of claim 2, wherein the microchannel texture is formed by geometric shapes.
 5. The polishing pad of claim 1, wherein the polishing pad is of unitary structure.
 6. The polishing pad of claim 1, wherein the polishing pad is a multilayer polishing pad.
 7. The polishing pad of claim 6, wherein the multilayer polishing pad comprises a polishing layer and at least one of the following, a backing layer and a subpad layer.
 8. The polishing pad of claim 1, wherein the polishing pad is a less rigid pad, defined as having a load of about 0.4 lbf or less at a 3 inch deflection using a 12″ long×5″ wide sample strip.
 9. The polishing pad of claim 2, wherein the microchannels have a channel depth from about 5 μm to about 250 μm.
 10. The polishing pad of claim 9, wherein the channel depth is from about 20 μtm to about 50 μm.
 11. The polishing pads of claim 2, wherein the microchannels have a channel pitch from about 0.1 mm to about 10 mm.
 12. The polishing pad of claim 11, wherein the channel pitch is from about 1 mm to 5 mm.
 13. A method of affixing a chemical-mechanical polishing pad to a platen surface comprising: (a) securing a platen adhesive layer having a textured surface to the polishing pad, (b) attaching the polishing pad to the platen surface by pressing the textured surface of the platen adhesive to the platen surface, wherein the textured surface of the platen adhesive allows air to escape and not being trapped between the platen surface and the polishing pad.
 14. (canceled) 